The simplest proof of who built the first atom bomb is who used it first. If
the Nazis had 2 bombs and denyav has stated they would have used at least one
even if they had to tansport it by boat or truck. Same for the Soviets.

You forget that they were "incomplete" in april 45,what Germans needed a couple
of more weeks or like Eisenhower implied in his book "Crusade in Europa" a
couple of more months.
For the Hirosima and Nagazaki bombs I always used term "Assembled in US from
German components.
I agree if they were complete in early april Nazis would use them even in
Berlin.
In April 45 Soviet were far behind Germans,the same for Manhattan project
We are talking about a Germany that was so deperate as to train people to fly
piloted V-1s on suicide missions. They didn't even use those either.

They were trying to delay the advance of allies for a couple of weeks by all
means till their S weapons,A bombs was only one component of S weapon
development program,were ready.